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This article will discuss string to integer conversion in Bash script. First, we will discuss the math operations on strings and then we will see how to convert a string to an integer.

Mathematical operations on strings

Let's start our discussion with this simple code:

x_value=1000
y_value=20
echo $x_value+$y_value

The output of this code may be unexpected. See the output:

1000+20

The command echo concatenates the variable x_value and the variable y_value with a plus sign. Probably you are not interested in getting this output; instead, you expect 1020 as the output.

Having discussed this issue, let us explore ways to avoid it and get the desired output.

Use the expr command to convert a string to an integer

This command is used to evaluate an expression and get the result. For example:

$ expr 12 - 8

The output of this command will be 4. We can use this command to get the desired result:

x_value=1000
y_value=20
expr $x_value + $y_value

The output of this script is 1020; however, note that a space is required between the variable and the operator. Otherwise, this command will also perform concatenation with the same result.

Use the double bracket ((...)) construct to convert a string to an integer

The double-brace constructor (( ... ))allows arithmetic expansion and evaluation; for example, x_value=$(( 6 - 2 ))x_value will be set to 4. We can use this construction to get the desired result.

Let's look at an example script:

x_value=1000
y_value=20
echo $(( x_value * y_value ))

The output of this script will be 20000.

Use the Basic Calculator (bc) command to convert a string to an integer

In Bash, the basic calculator (bc) is used to perform basic arithmetic calculations directly from the Bash command interface.

For example, we could write:

$ echo "12-4" | bc

The output is 8. We can use this basic calculator to get the results we need.

The code to solve our original problem using bc is as follows:

x_value=1000
y_value=20
echo $x_value-$y_value | bc

The output is 980. In this expression, no spaces are required, as they are enforced in the expr command.

Convert a string to an integer using awk command

awkis a precompiled command that allows the user to print formatted expressions containing variables, numeric functions, string functions, and logical operators. You can use this command in a number of ways.

For example, if you want to print a message with some formatted numeric calculations, you can use the echo command with the awk command, for example:

$ echo salary= 40000 10 | awk '{print $1 $2+$2*$3/100}'

In this command, we want to print the salary, where the salary includes a 10% bonus. Here, salary=is our first parameter. We use it by writing $1.

Likewise, 40000 is the second argument used to write $2; similarly, $3 is a placeholder for the third argument (i.e., 10).

The output of this command is:

salary=44000

We can use the awk command to solve our original problem:

x_value=1000
y_value=20
echo $x_value $y_value | awk '{print $1 + $2}'

The output will be 1020, where x and y are the two parameters received by the awk command. Perform the calculation accordingly.

Use perl...print or perl...say to convert a string to an integer

We have print or say option in perl command. The difference between print and say is that print does not wrap, the next output will appear in the same line, whereas say command wraps.

For example:

x_value = 5
perl -E "print $x_value"
echo "*"
perl -E "say $x_value"
echo "*"

The output will be:

5*5
*

请注意, the second asterisk is printed on the next line because the newline character is said rather than printed.

Therefore, we can use perl with print or say to get the output we need:

x_value=1000
y_value=20
perl -E "print $x_value+$y_value"

The output will be 1020.

Convert a string to an integer using Python

Python has a print statement that evaluates and prints an expression.

For example:

python -c "print 5 * 4"

The output will be 20. We can use this to get the desired result.

The code looks like this:

x_value=1000
y_value=20
python -c "print $x_value * $y_value"

The output is 20000.

We have various ways to convert a string into an integer variable to perform mathematical operations. Here, we have provided six different ways and you can use any of them according to your choice.